The weights room in the Europa Gym Club is full of the sound, and smell, of men. There are a dozen of them in the confined space, some lifting, some spotting, and some intensely contemplating their barbells. Ivan, a ginger-haired lad of 18, is straining at every visible point to keep his 91kg bar above his head. He lets it clatter to the floor, his face the colour of uncooked salmon. "See what he's lifting?" asks coach Andy Callard. "Zoe can lift 2.5kg more."

We turn to look at the young girl slouched against the wall, listening to her iPod between reps. Zoe Smith, 15, is currently the best female weightlifter in Britain. And at 5ft 2in, she is considerably shorter - and svelter - than Ivan.

Since Smith took up the sport two years ago, she has broken every British record - junior and senior - in her 53kg category. In December she was named Olympic Athlete of the Year after winning gold at the Commonwealth Youth Games in India. And three years from London 2012, she's already considered one of Britain's best young prospects. "I'm surprised by what I'm lifting now," she admits as she prepares for another set.

Whatever your image of a weightlifter, Smith, with her compact features and angular hair, probably doesn't meet it. A gymnast since she was eight, she says she had as much interest in "big 20-stone blokes" as the average teenager, until she was asked to make up the numbers for a London tournament at her gym in Erith, Kent. Her mum, Niki, didn't want her to get involved. "She thought it would take me away from my gymnastics," laughs Smith. "And obviously it did."

Callard - who won Commonwealth gold in 1994, the year Smith was born - spotted her potential immediately. "She wasn't just strong, she picked up the technique really fast," he says. "This year at the British Schools Games she won lifting 50kg more than the runner-up. That's like running the 100m and finishing 50m ahead."

Today, Smith's workout is comparatively light - two hours with low weights, in varying combinations of squats, pulls and lifts. The coach doesn't want his pupils distracted by cardiovascular exercise; the only machines in the room are the lifters. Smith comes here five times a week, a single female amid the boisterous fraternity. Every few seconds, your ears are assaulted by the clanking of someone dropping their barbell, followed, almost as noisily, by the backchat.

"It can be intimidating even for an adult," says Callard. "For a teenage girl to cope with it is impressive." Smith is shy and quietly spoken, but noticeably less so around the lads. "It's brought a lot of confidence out in me really," says Smith, "because if I don't learn to stick up for myself I'll just be an-nih-ilated."

Smith always had a natural strength. At 12 months old, she climbed her parents' door frames: "I'd wrap my hands and feet around them and push myself up and hang off the door handle." And while six years of gymnastics helped hone her muscles, she found she was even better with her feet firmly on the floor. "Weightlifting is more my thing, I've got that explosive power. I was never graceful enough to be a gymnast."

Since winning her first competition without realising it - "Now I know that if you're the last person standing it means you've won," she smiles - Smith has broken so many records, in so many countries, that she admits she loses track (the current figure is 109). She prefers the "snatch" (personal best: 72kg) to the "clean and jerk" (personal best: 87kg). Perhaps more importantly, she is also shattering weightlifting's unappealing stereotype. On the walls of the gym are grotesque images of female bodybuilders, their veiny bulges throwing Smith's petite physique into sharp relief. "My arms are getting a bit bigger," she says, "but not huge. And I've actually lost weight off my stomach. I'm really happy with the way I look."

Nor is she on a diet of shakes and supplements. Ask if she takes anything to help her along, and she answers sweetly that her mum gives her echinacea to stop her getting colds, "because that would be a naff reason to miss a tournament". She eats healthily, and only goes on a "mad diet phase" if she needs to make her weight. "Boxers only have to make the weight the night before," she complains. "I have to wait until the morning. So I literally have about two hours to rehydrate and to eat."

Next year will bring Smith's first major tournament as a senior - the Commonwealth Games in Delhi. She will be 16, facing a field of women often 10 to 20 years older than her, but says she won't be daunted, because she's used to being the youngest. What has the reaction been from her competitors? "Disbelief, I think." She speaks with an innocent mix of honesty and humility; Smith's confidence is born not of her ego but of her experience. "If nothing's gone wrong until now," she says, "it can carry on going right."